1. Technical Field
The present invention relates to an apparatus for correcting a temperature sensing (or measurement) signal and more particularly, to an apparatus for correcting a temperature sensing signal, which is capable of determining a value of voltage drop generated in an output limiting diode included in an IGBT temperature sensor by calculating a value of a current flowing through the output limiting diode and capable of correcting an error of a temperature sensing signal output from the IGBT temperature sensor, which is caused by the voltage drop of the output limiting diode, by increasing a voltage of the temperature sensing signal by the voltage drop value.
2. Description of the Related Art
In general, an IGBT (Insulated Gate Bipolar Transistor) refers to a high power switching transistor having a fast switching function to block or conduct a flow of electricity.
The switching function requires a dedicated part having a high operation speed and a low power loss for a product requiring a precise operation, although it may be implemented with other parts or circuits.
However, an existing switching semiconductor transistor has a demerit that it has a complicated circuit configuration and a low operation speed although it is inexpensive. In addition, an existing switching semiconductor MOSFET (Metal Oxide Semiconductor Field Effect Transistor) has a demerit that it is expensive although it consumes low power and has a high operation speed. IGBT is evaluated as a product having only the merits of the above-mentioned transistor and MOSFET. Accordingly, the IGBT is being used as a switching device in a variety of power converters such as an inverter, a converter and so on.
In typical, an IGBT for converting power of a high voltage and a large current generates hot heat due to resistance, which has an effect on stability and power efficiency of a power converter.
Accordingly, the IGBT is provided with an IGBT temperature sensing device for measuring (or sensing) a temperature of the IGBT by using an NTC (Negative Temperature Coefficient) thermistor.
The NTC thermistor is a thermistor whose electrical resistance is continuously changed with a negative temperature coefficient, and is used as a temperature sensor using this characteristic.
FIG. 1 is a circuit diagram of a conventional IGBT temperature sensing device.
Referring to FIG. 1, a conventional IGBT temperature sensor 10 includes a temperature sensor 11, a signal selector 12 and an AD input part 13.
An NTC thermistor RNTC of the temperature sensor 11 is changed in its resistance with a change in temperature of the IGBT. A first voltage distributing resistor R1 and a second voltage distributing resistor R2 of the temperature sensor 11 distribute a voltage of a driving power supply Vcc to the NTC thermistor RNTC according to a preset ratio.
Accordingly, a temperature sensing signal is output to an output limiting diode D1 according to the change in resistance of the NTC thermistor RNTC.
The output limiting diode D1 outputs the temperature sensing signal to the signal selector 12 only when a voltage of the temperature sensing signal is equal to or higher than a preset voltage.
The signal selector 12 compares a voltage of a previously received temperature sensing signal with a voltage of a recently received temperature sensing signal. If the voltage of the recently received temperature sensing signal is higher than the voltage of the previously received temperature sensing signal, the signal selector 12 outputs the recently received temperature sensing signal to the AD input part 13.
The AD input part 13 converts an analog voltage value of the temperature sensing signal to a digital voltage value which is then output to the outside or an IGBT controller.
The conventional IGBT temperature sensor 10 uses the output limiting diode D1 conducted only when a driving voltage is applied to output only a temperature sensing signal having a voltage equal to or higher than the preset voltage value.
In this case, when the output limiting diode D1 is conducted in a forward direction, a voltage drop occurs in the output limiting diode D1. Accordingly, in the conventional IGBT temperature sensor 10, a voltage difference occurs between a temperature sensing signal before being input to the output limiting diode D1 and a temperature sensing signal output from the output limiting diode D1, which may cause an error in a measurement of the IGBT temperature due to the voltage difference.